Mareks to keep recovered hen, advise needed!

Hi
About 2 months ago I had two young chicks about 5 weeks old suddenly off balance, sitting on hocks etc. I culled these chicks and those with them. I assumed it was Marek's. I know once these chicks got to this stage they could already have infected my other hens even if they didn't show signs.
I don't believe I have had anything further since then until a couple of days ago when I saw a hen sitting down and not getting up in the dust bath area. She is approx 3 months old. I picked her up and she was just weak, no apparent paralysis in legs but the main thing was she could not keep her head up, it was not twisted, just appeared weak and I noticed she was slightly wobbly and shaky in the head with her mouth opening and closing rapidly at times. She seemed disorientated to some extent. She would not eat or drink.
I put her in isolation and the next morning when I checked on her I thought she was dead, lying flat down, neck stretched out and eyes closed.
I did not touch her and thought I would just get my son to bury her when he got home. When he did get home and he went to get her, she was not dead and put her head up slightly when he went to touch her. So that night I held her over the water and held her head so she could drink but she would not eat. The next morning she looked slightly better and by that afternoon she was up on her feet and seemed lots better, next day back to normal.
She did come from a large penned area with about 30 other hens and roosters in it that range in age from 3-5 months and it does get a little hectic in there at feeding time as they all clamper at the pen walls when I bring the food over and I wondered if she got injured somehow or if this is just another manifestation of Marek's.
So what do I do now is the question.
Firstly does anyone here think this is Marek's or not?
Secondly, If it is Marek's and I put her back with the flock then she will be a carrier and shed it, yet if she has it so does probably the rest of the flock anyway. I am not sure if I still should cull her or not.
Others on here know more about this than me and about breeding for resistance and I wonder if her surviving it would actually be a good thing or not to put her back with the rest of them.
Advise please.
Thanks to all who answer. Me

That's quite a story. Your hen made such a dramatic recovery after you gave her some water, it leads me to believe she was dehydrated and this was not Marek's. While birds do recover, I have never heard of a miraculous, instantaneous recovery from Marek's.

You are assuming your chicks had Marek's. Without necropsy testing, you can't know that's what was the cause of their illness. There are other things such as vitamin deficiencies that cause similar symptoms.

If it was Marek's, and if this hen has it, then your flock has been exposed. It's that contagious. In the future, if you should have a chicken sicken and die, I urge you to get a necropsy so you will know exactly what you're dealing with.

It is not vitamin deficiency I am sure of that with what I feed and they were free ranging enjoying many bugs etc. I also could not get them tested as it was on a Friday night when I saw them and did not want them to suffer as they appeared to be doing so put them down at that time. I was going to autopsy the hen but of course she has survived but will do so with the next one, if there is a next one.

It could be dehydration but there was ample water in the pen where she was and it was fresh and easy to get to, there was also lots of shade.
Do they still get dehydration when they can get to water easily?

Anyone else have an opinion on whether to put her back with the flock or not?

Yes. If the hen was being bullied away from food and water, she could have gotten dehydrated, especially if it's late summer where you live. You did mention that things appeared hectic in the flock preceding this event. Chances are good this hen is low in the pecking order and has been intimidated by the others. I would observe the flock dynamics when you return her.

Vitamin deficiencies can occur even when a balanced diet is provided, in chicks as well as older individuals. For some reason, they aren't assimilating all the necessary nutrients. Riboflavin and vitamin E deficiencies can cause the symptoms you described in your chicks, mimicking Marek's. Also, selenium deficiencies can also cause neurological symptoms. When these vitamins are given, the symptoms quickly disappear. it's one way to rule out Marek's.

Just in case someone is interested in this thread I thought I would share the following information.

Mareks is quite a sneaky disease, apparently it can in carrier birds create an environment that means the birds do not process vitamins efficiently.

There were some cases on the net that I came across where sick birds where given vitamins assuming that was the issue and yes the birds recovered (remember that this is a virus so strengthening the immune system can help) anyway soon after the birds got sick again. All times the birds were autopsied and it was found to be Mareks.

Anyway, it would appear that usually symptoms do not reverse as quickly as they did in my hen so I am thinking it may have been dehydration as she was a smaller hen and maybe she did get bullied away from the water. I am going to release her back to an area where she can free range and hope I am making the right decision.